.img > img {
    width: 100%;
}
.center-2 {
    height: 30%;
}
.introduce {
    width: 95%;
    margin: 0 auto;
    margin-bottom: 2%;
    text-indent: 30px;
}
.introduce-3 {
    margin-bottom: 5%;
}
.introduce-3 > div {
    background: #c8c8ca;
    width: 25%;
    height: 300px;
    display: inline-block;
    margin: 0 3%;
}
.introduce-3 > .f {
    margin-left: 6%;
}